Automatic trimmer head

ABSTRACT

A trimmer head, comprising: a casing  21, 22,  a supporting device  31, 32  for a cutting wire spool, which supporting device ( 31, 32 ) is arranged within the casing ( 21, 22 ) and movable between an engagement position, wherein it is rotatingly solid with the casing ( 21, 22 ), and a free position, wherein it is not rotatingly solid with the casing ( 21, 22 ). The head further comprises coupling means  41,42,  which are so configured as to make the casing ( 21, 22 ) and the supporting device ( 31, 32 ) rotatingly solid with one another in the engagement position, engagement means ( 43 ) which are so configured as to allow displacement of the supporting device ( 31, 32 ) from the free position to the engagement position and release means ( 51, 52 ) configured for moving the supporting device ( 31 ) from the engagement position to the free position, said release means ( 51, 52 ) being activated under the effect of the centrifugal force due to rotation of the trimmer head. The supporting device  31  comprises a lower disk ( 31 ) and an upper disk ( 32 ) which are independent of one another.

FIELD OF THE INVENTION

The present invention has for an object a trimmer head. The invention particularly relates to a head provided with an automatic cutting wire unwinding device.

BACKGROUND OF THE INVENTION

Several examples of heads of this type are currently available on the market. These heads comprise a casing internally of which a winding-reel is housed for winding a wire cutting spool. Two portions of the cutting wire protrude outwardly the casing through dedicated openings. The winding-reel is associated to the casing and can take on an engagement position, wherein it is rotatingly solid with the casing, and a free position, wherein it can rotate with respect to the casing. Notoriously, the free position of the winding-reel is exploited to cause unwinding of the wire spool with the purpose of restoring the length of the cutting wire portions which protrude outward of the casing. The automatic cutting wire unwinding device allows essentially to move the winding-reel between the engagement position and the free position without being necessary to stop the trimmer head and perform manual operations.

The activation of the automatic unwinding device exploits the rotational speed variation of the head resulting from the shortening, due to wear, of the wire portions which protrude outward of the casing. The shortening of such portions reduces the moment of inertia of the head, which consequently increases its rotational speed. The automatic cutting wire unwinding device is activated as a result of the increased centrifugal force acting on one or more masses suitably placed inside the head. The activation of the unwinding device causes a lengthening of the protruding wire portions and an increase of the moment of inertia of the head. Hence, the head slows down, thereby reducing the force of inertia acting on the masses which cease to activate the unwinding device.

The heads currently available therefore provide use of a winding-reel whereon the cutting wire is wound. Once the cutting wire is used up, a new cutting wire needs to be wound onto the reel in order that the terminated spool can be restored. This operation, which is carried out without the head having to be disassembled, is rather long in that a manual rotation of the winding-reel is required until complete winding of the fresh spool thereon.

An example of a head currently available is described in WO2013/179318.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a trimmer head which allows to overcome the drawbacks of the heads available at present.

One advantage of the trimmer head is that replacement operations of the cutting wire spool are simplified and speeded up.

Another advantage of the trimmer head is that it is particularly lightweight and compact.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of a preferred embodiment of the invention illustrated by way of non-limiting example in the appended figures wherein:

FIG. 1 shows a sectional view of the trimmer head illustrated on a plane containing the main rotational axis (X) of the trimmer head;

FIG. 2 shows a first exploded axonometric view of the trimmer head;

FIG. 3 shows a second exploded axonometric view of the trimmer head; and

FIG. 4 shows an axonometric view of a cutting wire which may be used in the trimmer head of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The head according to the present invention comprises a casing (21, 22), designed to be coupled to a driveshaft for rotating about a main axis (X). The casing (21, 22) is provided with one or more openings (A) in order to afford passage of respective end portions of the cutting wire (W). A supporting device (31, 32) for a cutting wire spool is housed inside the casing (21, 22).

The supporting device (31, 32) is movable between an engagement position, wherein it is rotatingly solid with the casing (21, 22), and a free position, wherein it is not rotatingly solid with the casing (21, 22). In a known manner, in the free position of the supporting device (31, 32), a relative rotation between the casing (21, 22) and the supporting device (31, 32) itself is produced during rotation of the head. This relative rotation is aimed at causing unwinding of a given portion of the cutting wire owing to which the portions that became detached during use can be restored.

Coupling means (41, 42) are configured for making the casing (21, 22) and the supporting device (31, 32) rotatingly solidly constrained with one another in the engagement position. In a preferred embodiment, the coupling means comprises a toothed profile (41, 42) interposed between the supporting device (31, 32) and the casing (21, 22). In particular, the toothed profile comprises a first toothing (41), which is integral with the supporting device (31, 32), and a second toothing (42), which is integral with the casing (21, 22). In the engaged position the two toothings (41, 42) are mutually engaged, thereby making the casing (21, 22) and the supporting device (31, 32) rotatingly solidly constrained with one another. In the free position the two toothings (41, 42) do not interact with each other.

In the preferred embodiment, the first toothing (41) protrudes downwardly of the supporting device (31, 32), while the second toothing (42) protrudes upwardly from a bottom surface of the casing (21, 22), frontally to the first toothing (41). The supporting device (31, 32) is movable along the main axis (X) between the engaged position and the free position thereof. The engagement position, in which the toothings (41, 42) are mutually engaged, is less than the free position in which the toothings (41, 42) are disengaged.

Engagement means (43) are configured for displacement of the supporting device (31, 32) from the free position to the engagement position. In the preferred embodiment such engagement means (43) comprises an elastic element, which is so configured as to urge the supporting device (31, 32) towards the engagement position. The elastic element (43) is particularly interposed between the shell (21, 22) and the supporting device (31, 32), above the supporting device (31, 32) itself. The elastic element (43) is compressed such that the supporting device (31, 32) is urged downwards.

Release means (51, 52) are predisposed for moving the supporting device (31, 32) from the engagement position to the free position. Such release means (51, 52) are so configured as to be activated under the effect of the centrifugal force due to rotation of the head.

In particular, the release means (51, 52) comprises one or more masses (52) arranged within the casing (21, 22) in an eccentric position with respect to the main axis (X) and movable along at least a radial direction with respect to the main axis (X) owing to the centrifugal force. Each mass (52) is predisposed for interacting with the supporting device (31, 32) and for displacing it from the engagement position towards the free position due to its radial movement taking place away from the main axis (X).

In the preferred embodiment of the head, each mass (52) is slidable along a track (53) which is oriented radially with respect to the main axis (X). Each track (53) is disposed on a bottom surface of the casing (21, 22).

The release means (51, 52) comprises an inclined surface (51) placed in contact with the mass (52). In particular, the inclined surface (51) is disposed below the supporting device (31, 32). Each mass (52) is interposed between the inclined surface (51) and the casing (21, 22). The inclined surface (51) exhibits a descending inclination while proceeding away from the main axis (X), so that the supporting device (31, 32) tends to be pushed upwards by the masses (52) which slide away from the main axis (X) owing to the centrifugal force. In this way, as the cutting wire becomes consumed and the moment of inertia of the head is reduced, the rotational speed of the head is increased, and together with it the centrifugal force acting on the masses (52), whose thrust on the supporting device (31, 32), when the head exceeds a certain rotational speed, exceeds the downward thrust exerted by the spring (43). In such conditions, the supporting device (31, 32) moves upwards until the free position is reached, wherein it can rotate with respect to the casing (21, 22) thereby providing to unwind the cutting wire progressively. This causes an increase of the moment of inertia of the head which slows down to the point where the centrifugal force acting on the masses (52) is no longer sufficient to overcome the thrust of the spring (53). In such conditions, the supporting device (31, 32) returns downwards in its engagement position.

The supporting device (31, 32) comprises a lower disk (31). The inclined surface (51) is located below the lower disk (31), between the outer edge and an intermediate portion of the lower disk (31). Also the first toothing (41) protrudes downwards to the lower disk (31).

The supporting device (31, 32) further comprises an upper disk (32) which is disposed within the casing (21, 22), opposite to the lower disk (31). In particular, the upper disk (32) is arranged above the lower disk (31) at a certain distance therefrom so as to delimit a housing for a cutting wire spool. The upper disk (32) is movable relative to the casing (21, 22) along the main axis (X). The engagement means (43), i.e. the spring (43), are interposed between the casing (21, 22) and the upper disk (32). In this way the engagement means (43) operates on the lower disk (31) through the upper disk (32) and the cutting wire spool housed between the lower disk (31) and the upper disk (32).

The lower disk (31) and the upper disk (32) are mutually independent. In particular, each of them is movable along the main axis (X) independently from the other. The fact that the disks (31, 32) are independent from one another, allows use of a spool (S) of the cutting wire (W) coiled up into a flat spiral. The spool is compressed between the two disks (31, 32), thus remaining steadily in a flat configuration. This type of spool, wherein the loops of wire are placed alongside and substantially intersected by a same median plane being perpendicular to the main axis (X), is particularly compact and lightweight and can be swiftly replaced.

The lower disk (31) is provided with a central pin (33) which protrudes upwards concentrically to the main axis (X) and is intended to be inserted into a central opening (SO) of the spool which is delimited by the innermost loop. The central pin (33) is provided externally with engagements, not shown in detail, intended to come into contact with the innermost wire loop of the spool, in order that the wire spool and the lower disk (31) become solidly constrained with one another with respect to the rotation about the main axis (X).

The cutting wire (W) preferably exhibits an inner engagement portion (P1) disposed longitudinally on an inner side of the wire loops and an external engagement portion (P2) arranged longitudinally on an outer side of the wire loops. Such engagement portions (P1, P2) are predisposed for engaging each other at the adjacent loops, so that the spool (S) is maintained combined in the flat configuration. The central pin (33) of the lower disk (31) is inserted into the central opening (SO) of the spool (W), so that the inner engagement portion (P1) becomes tightened in contact with the central pin (33). Preferably, the inner engagement portion (P1) is in the form of a longitudinal groove, whereas the external engagement portion (P2) is in the form of a longitudinal projecting rib, which is counter-shaped to the longitudinal groove (P1).

Two or more spools (S) overlapping one another along the main axis (X) may be arranged between the lower disk (31) and the upper disc (32).

Advantageously, the casing (21, 22) comprises a lower shell (21) and an upper shell (22) being separable from one another. A rapid coupling and detachment device (R), for example with snap coupling, can be interposed between the two shells (21, 22) for easy detachment and coupling thereof. The lower shell (21) and the lower disk (31) are constrained to one another so that the lower disk (31) can not be separated completely from the lower shell (21). To this end the lower shell (31) is provided with a central through opening (36). The lower disk (31) has a hub (34), which is concentric to the main axis (X), which is rotatably and slidably arranged through the central opening (36). An abutment element (35) is associated with the end of the hub (34). Such abutment element (35) exhibits a head (37) which is disposed outside the central opening (36), whose diameter is greater than the internal diameter of the central opening (36).

The overall extension of the hub (34) and the abutment element (35) along the main axis (X) is such as to enable displacement of the lower disk (31) between the engagement position and the free position.

Preferably also the upper shell (22) and the upper disk (32) are constrained to one another so that the upper disk (32) cannot be separated completely from the upper shell (22). In particular the disk (32) is secured to the upper shell (22) via two pins (23) which extend parallel to the main axis (X) from a bottom surface of the upper shell (22). The pins (23) are passing through holes which are afforded in the upper disk (32), so that the upper disk (32) can slide parallel to the main axis (X) with respect to the upper shell (22). Owing to the presence of screws or the like placed at the end of the pins (23), the upper disk (32) is prevented from slipping off completely.

During rotation of the head, in the free position of the lower disk (31) a relative rotation between the lower disk (31) and the upper disc (32) is thus produced, in that the latter remains solidly constrained in rotation to the casing (21, 22). This relative rotation promotes easy unwinding of the cutting wire, in that it makes easier the separation between the loops of the spool.

Owing to the presence of the disks (31, 32) being mutually independent, replacement of the spool of wire occurs in an extremely quick and easy manner. In order to have full access to the supporting device (21, 22) and in order that a new spool of wire is positioned on the lower disk (31), it is indeed sufficient to separate the two shells (21, 22). 

1. A trimmer head comprising: a casing (21,22) designed to be coupled to a driveshaft for rotating about a main axis (X); a supporting device (31,32) for a cutting wire spool, which supporting device (31,32) is arranged within the casing (21,22) and movable between an engagement position, wherein it is rotatingly solid with the casing (21,22), and a free position, wherein it is not rotatingly solid with the casing (21,22); coupling means (41,42), which are so configured as to make the casing (21,22) and the supporting device (31,32) rotatingly solid with one another in the engagement position; engagement means (43) which are so configured as to allow displacement of the supporting device (31,32) from the free position to the engagement position; release means (51,52) configured for moving the supporting device (31) from the engagement position to the free position, said release means (51,52) being activated as a result of the centrifugal force due to rotation of the trimmer head; characterized in that: the supporting device (31,32) comprises a lower disk (31) and an upper disk (32) which are independent of one another.
 2. A trimmer head according to claim 1, wherein the casing (21,22) comprises a lower shell (21) and an upper shell (22) separable from one another.
 3. A trimmer head according to claim 2, in which the lower shell (21) and the lower disk (31) are solidly constrained to one another so that the lower disk (31) cannot be separated completely from the lower shell (21).
 4. A trimmer head according to claim 2, wherein the upper shell (22) and the upper disk (32) are solidly constrained to one another so that the upper disk (32) cannot be separated completely from the upper shell (22).
 5. A trimmer head according to claim 1, wherein the release means (51,52) comprises at least one mass (52) arranged within the casing (21,22) in an eccentric position with respect to the main axis (X) and movable along at least one radial direction with respect to the main axis (X) owing to the centrifugal force; the mass (52) is predisposed for moving the supporting device (31,32) from the engagement position to the free position as a result of its radial movement taking place away from the main axis (X).
 6. A trimmer head according to claim 5, wherein the release means (51,52) comprises an inclined surface (51) placed in contact with the mass (52).
 7. A trirnmer head according to claim 6, wherein the inclined surface (51) is disposed below the lower disk (31); the mass (52) is interposed between the inclined surface (51) and the casing (21,22).
 8. A trimmer head according to claim 1, wherein the engagement means (43) comprises an elastic element (43) which is so configured as to urge the supporting device (31) towards the engagement position.
 9. A trimmer head according to claim 1, wherein the coupling means comprises a toothed profile (41,42) interposed between the supporting device (31) and the casing (21,22).
 10. A trimmer head according to claim 9, wherein the toothed profile (41,42) comprises a first toothing (41) which protrudes downwardly at the lower disk (31), and a second toothing (42) which protrudes upwardly from the casing (21,22); when the supporting device (31) is in the engagement position thereof, the toothings (41,42) interact with one another thereby preventing relative rotation between the supporting device (31) and the casing (21,22), whereas when the supporting device (31) is in its free position, the toothings (41,42) do not interact with one another.
 11. A trimmer head according to claim 1, comprising a spool (S) of wire (W) coiled up into a flat spiral, wherein the loops of the wire are alongside each other and substantially intersected by the same median plane perpendicular to the main axis (X), said spool (S) being compressed between the two disks (31,32).
 12. A trimmer head according to claim 11, wherein the cutting wire (W) has an inner engagement portion (P1) disposed longitudinally on an inner side of the loops; the lower disk (31) is provided with a central pin (33) that protrudes upwards concentrically to the main axis (X) and is intended to be inserted into a central opening of the spool delimited by the innermost loop so that the inner engagement portion (P1) becomes tightened in contact with the central pin (33).
 13. A trimmer head according to claim 11 comprising two or more spools (S) which are overlapping one another along the main axis (X). 